HomeMy WebLinkAboutWPO201400071 Review Comments 2014-11-20lM
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November 20, 2014
Mr. John Anderson
County of Albemarle
Department of Community Development
401 McIntire Road, Room 227
Charlottesville, VA 22902
RE: Old Trail Block 12 & 15 — Final Site Plan (WP0201400071 and WP0201400047)
Dear Mr. Anderson,
I have reviewed and addressed your comments. The individual responses to the comments for
Block 12 are below.
A. VSMP: SWPPP and Pollution Prevention Plan — Block 12 (WP0201400071) (Section 17-405)
(The Virginia stormwater management program, stormwater pollution prevention plan application
and documents)
Refer to Block 15 comments; Comments are virtually identical. Oct-2 meeting scheduled for
questions.
Responses to comments concerning the SWPPP are addressed in the WPO comments for
Block 15.
B. VSMP: SWPPP: Stormwater Management Plan — Block 12 (WP0201400071)
Refer to Block 15 comments. WP0201400047 SWM comments (2-8) apply to Blocks 15 and 12
equally.
2. Attach or transfer relevant sheets, elements and details of block 14 approved WPO
(WP0201300021) to current application to lend guidance and clarity during WPO review of block
15, during bonding, inspection, and construction. WPO plans for block 15 may not be approved by
simple reference to an approved WPO without transferring relevant information. To reiterate, please
include plan sheets listed below for purposes of guidance and clarity (not analysis), since nearly all
block 15 post -development runoff routes to an approved modified (future) bioretention facility. (At
present, and for some time, the facility will serve as a sediment basin). Transfer sheets 4, 5, and 6 of
approved WP0210300021 plan set (March 20, 2013) without change. Please label each sheet as a
plan sheet taken from approved WP0201300021. (Rev. 1) Comment partially addressed: as
follow-up: please label each sheet as originating with WP0201300021.
Each sheet now has a note in the lower right-hand corner stating "Taken from WP0201300021
In addition, from sheet 2 of March 20, 2103 plan set, attach or transfer: sediment basin narrative,
sediment basin schematic elevations detail (including design elevations with emergency spillway),
and plan view of basin — label this information taken from approved WPO201300021. Further,
please label major contours (640', 650'). Confirm and label existing base of sediment basin elevation
= 635.0'. (Rev. 1) Comment partially addressed. As follow-up to 10-Sept discussion, please
remove sheet 2 of WP0201300021. The appearance of existing Block 14 ESC measures may
confuse. Instead, from WP020130002 I /sheet 2, please include (with both Block 15 and Block 12
VSMP plans): Sediment Basin Narrative; Sequence of Construction; Sediment Basin Schematic
Elevations. These details line WP0201300021 modified sediment basin design data to a future
bioretention facility.
Sheet 2 from WP0201300021 was removed from the plan set. I copied the Sediment Basin
Narrative; Sequence of Construction; Sediment Basin Schematic Elevations from sheet 2 of
WP0201300021 and put them on the EC Narrative sheet for both Block 15 and Block 12.
Note/see New. #4, below: Bioretention has been approved for Blocks 14 and 11, not the entire 19.25
Ac. Area shown on sheet 5, WP0201300021. While WP0201300021 provides perimeter ESC for
Block 12 and most of Block 15, and provides SWM for Blocks 11 and 14, it does not provide future
development (Block 15 and 12) stormwater control beyond 46,286 s.f. of impervious area and
158,208 s.f. of lawn/cultivated turf area — ref. Short Version BMP Computation spreadsheet detail
shown on Sheet 5, WP0201300021.
New:
4. WP0201400021 provides SWM control for 46,286 s.f. offuture development impervious area.
WP0201400021 schematic of Blocks 11, 14, 12 & 15, as well as drainage area defined as 19.25 Ac., shows
future impervious area = 125,000 s.f. (12 & 15). With revised WP0201400047, please compare 46,286 s.f.
impervious and 158,208 s.f. lawn (area) available under WP0201300021 with proposed Block 15
development. If proposed impervious/lawn exceeds what is available under WP0201300021, provide
treatment. Note: Please see water quality narrative, bullet 3, sheet 5, WP0201300021: 8,700 sf x 12 in/ft =
104,400 cu.in; 104,400 ins, under this methodology, provides WQ control for'Y2" runoff for 208,800 sf of
impervious area. Average of 208,800 and 348,000 sf = 278,400 sf. Taking Block 11 and 14 impervious areas
into consideration, 46,286 s.f. is available — not 50,330 s.f. listed in bullet 3. This calculation does not affect
Block 11 or 14 approvals, but bioretention basin (treatment) volume available for future (Block 15 and 12)
development is central to current reviews. We discussed this briefly 24-Sept-14.
The proposed impervious area for Block 12, Phase 1 = 33,308 s.f., which is less than the 46,286 s.f. of
impervious area that is allowed with WP0201300021.
5. Part II-B water quality criteria appear to apply to stormwater facility design of future development, to Block
15 areas not covered by WP0201300021 (ref. 9VAC25-870-63). Please utilize VaRRM spreadsheet design
methodology for areas not covered under WP0201300021.
All of the area for Block 12, Phase 1 is covered under WP0201300021.
6. In reporting post -development characteristics for use with VaRRM (or Short Version BMP), CN, drainages,
and land use/cover (including future Blocks 17, 18) should be checked. Fielding Run Drive is east boundary
of Block 15, and appears a divide, with areas just SW and to the east drainage east. It appears that proposed
contours do not allow runoff from certain areas within the 19.25 Acreage on sheet 5 (WP0201300021) to
reach the modified sediment basin/future bioretention facility. Underlying suppositions bear review. It
appears a portion of runoff from `current' (9.32 Ac.) and `additional' (9.93 Ac) areas depicted as reaching the
modified facility does not. Figures used to show compliance for Blocks 11 and 14 appear problematic or
invalid, and require revision to show SWM compliance for Blocks 15 and 12.
in
The entire impervious area proposed with the WPO plan for Block 12, Phase 1, is covered under the
WP0201300021 plans.
7. With revised WP0201400047, please furnish existing conditions with soil types/boundaries.
The existing conditions sheet, which shows the soil types and boundaries, is now included in the plan set.
8. Furnish pre -/post -development drainage area maps.
Because the impervious area proposed with the Block 12, Phase 1 plans is covered under the
WP0201300021 plans, I feel that showing the pre -/post -development drainage area maps is not necessary
for the WPO plans for Block 12, Phase 1.
C. VSMP: SWPPP: Erosion Control Plan — Block 12 (WP0201400071) — The erosion control plan
content requirements can be found in County Code section 17-402.
Provide diversion dike or ditch, west side of modified sediment basin, sheet 3.
A 94 foot diversion ditch is now proposed to allow runoff of the western side of the site to drain
into the modified sediment basin.
2. Revise CE to paved CE with wash rack, sheet 2.
The "Erosion and Sediment Control Legend" on sheets 3 and 4, now states that the CE symbol is a
"Paved Construction Entrance with Wash Rack". The detail for a paved construction entrance
with a wash rack is on sheet 7.
3. Revise 668' contour to 666', lower right quadrant, sheet 2, near Future Development Area label.
Grading labels revised.
4. Label all drainage easements beyond public RW PRIVATE. Comment applies to Blocks 12 and 15 —
please check labels carefully (existing/modified sediment basin, Rowcross St, Court Mont Way,
Private Alley `A'), and please accept apology for error. This will be a standard item of review with
future VSMP plans. Easements beyond public RW are Private. (Section 18-32.7.4.2.a.1)
Revised accordingly.